nixpkgs' proton-ge-bin (the package wired into programs.steam.extra-
CompatPackages via modules/desktop-steam.nix) registers in Steam's
compat-tool list under its versioned id, currently GE-Proton10-34.
steam-config-nix's README example uses the unversioned string
"GE-Proton", which on a fresh boot wrote that literal value into
localconfig.vdf — Steam resolved it to no installed tool and silently
fell back to bundled Proton 10. FH5 then launched on stock Proton,
which doesn't pick up PROTON_FSR4_UPGRADE the way GE does.
Drop both `compatTool` (per-app) and `defaultCompatTool` (global).
The wrapper-based launchOptions.env path is unaffected — env vars
still pass through to whatever Proton Steam ends up using. Tool
selection goes back to manual Steam UI > Properties > Compatibility.
A versioned pin (`compatTool = "GE-Proton10-34";`) would work but
couples the host config to whatever the proton-ge-bin nixpkgs entry
ships this week; not worth the maintenance.
Simon Gardling
774d748bfe